Regarding a transmission such as an automatic transmission mounted on a vehicle, studies have been made to (i) realize a weight reduction by omitting a torque converter in such a manner that when starting the vehicle, a start brake (so-called low reverse brake) constituting part of the transmission is caused to slip to realize smooth start while avoiding engine stall; and (ii) improve fuel efficiency of the engine in such a manner that a lockup clutch is engaged when starting the vehicle.
Specifically, the start brake includes: rotary-side friction plates attached to a predetermined rotating body and configured to rotate integrally with the rotating body; and fixed-side friction plates opposed to the rotary-side friction plates and configured not to rotate. By the engagement and disengagement of these friction plates, a connection status between a start gear and a driving source such as an engine is changed. Realizing the above smooth start by causing these friction plates to slip when starting the vehicle has been studied.
In a case where the brake is caused to slip when starting the vehicle, the number of times of the slip of the start brake becomes large. Therefore, to prevent the brake from increasing in temperature, the brake needs to be effectively cooled. According to a conventional brake described in, for example, PTL 1, lubricating oil is supplied to the friction plates during slipping.